Lethal infantile mitochondrial disease with isolated complex I deficiency in fibroblasts but with combined complex I and IV deficiencies in muscle

Abstract

A 2-month-old boy died of a lethal infantile mitochondrial disease with severe lactic acidosis and involvement of the CNS. Histochemical analysis of skeletal muscle showed that cytochrome c oxidase staining was lacking in all muscle fibers but was present in arterioles. Ragged red fibers were not seen, but some fibers showed excessive staining for succinate dehydrogenase. Biochemical analysis revealed a combined complex I and IV deficiency in skeletal muscle but only a complex I deficiency in his fibroblasts. Two-dimensional native SDS electrophoresis confirmed these enzymatic findings at the protein level. Analysis of mitochondrial translation products in fibroblasts revealed no abnormalities, and analysis of mitochondrial DNA in muscle showed no depletion, large-scale deletions, or frequently occurring point mutations. We conclude that this disease must have been the result of either a nuclear DNA mutation in a gene controlling the expression or assembly of both complex I and the muscle-specific isoform of complex IV or, alternatively, a heteroplasmic point mutation in a mitochondrial tRNA, which codon is used more often by mtDNA encoded subunits of complex I than by mtDNA encoded subunits of complex IV. A different degree of heteroplasmy in skeletal muscle and fibroblasts would then explain the curious heterogeneous tissue expression of defects in this patient.NEUROLOGY 1996;47: 243-248

Isolated complex I deficiency in children: Clinical, biochemical and genetic aspects

“…Differences in residual respiratory chain enzyme activities between tissues have been previously reported [Bentlage et al, 1996]. This is especially the case in the three FILA patients with isolated complex I deficiency in fibroblasts (complex IV activity repeatedly normal), whereas complex I and IV were decreased in muscle tissue.…”

“…In muscle tissue, enzyme assays were performed in crude homogenates or 600g supernatants of crude homogenates, while in fibroblasts mitochondrial enriched fractions were used. The enzyme assays performed in cultured skin fibroblasts were slightly modified according to procedures as described by Bentlage et al [1996]. We considered a patient isolated complex I deficient when the activity was evidently decreased below the reference interval (0.11-0.28 mU/mU cytochrome oxidase) in two different fibroblast preparations.…”

Mitochondrial Complex V Expression and Activity in Cystinotic Fibroblasts

“…Mitochondrial fractions of control and cystinotic fibroblasts were prepared as described before (6). Complex V activity was determined in presence and absence of specific inhibitor oligomycin (8 mg/mL) in mitochondrial fractions incubated with ATP (5 mM) as substrate (7).…”

The mitochondrial 13513G>A mutation is most frequent in Leigh syndrome combined with reduced complex I activity, optic atrophy and/or Wolff–Parkinson–White

“…Biochemical analyses of muscle and cultured fibroblast tissues was performed as described before. 13,14 All patients were tested for the presence of the m.13513G4A and m.13514A4G mutation in the mitochondrial ND5 gene. All selected subjects had tested negative for common pathogenic point mutations at nucleotide positions m.3243, m.8344 and m.8993 and single large mtDNA rearrangements (deletions or duplications).…”